1. Field of the Invention
This invention relates to methods and apparatus for improving the sensitivity and detection limits of UV fluorescence detectors.
More particularly, the present invention relates to methods and apparatus for improving the sensitivity and detection limits of fluorescence detectors which include a reaction cell having optical smooth and highly reflective internal surfaces that are preferably composed of a material that does not react with the sample or photo-excited components in the sample being analyzed.
2. Description of the Related Art
Fluorescence detectors such as UV fluorescent detectors generally include a reaction chamber where a sample to be analyzed is exposed to light from a source. The light is absorbed by certain components in the sample that then fluoresce. The fluorescence is measured by a detector such as a photomultiplier tube and the detector output is converted into a readable output.
One major deficiency of current light reaction chambers is that signal to noise ratios prevent reliable and reproducible determination of trace components much below about 1 ppm. Thus, there is a need in the art for an efficient, cost effective procedure for increasing the sensitivity and detection limit of fluorescent detectors.
This invention provides a light reaction cell for improving the sensitivity and detection limits of fluorescence spectroscopy including UV fluorescent spectroscopy where the cell includes a photo-reaction chamber having interior surfaces that are reflective to a desired light frequency (wavelength) range and preferably highly reflective and optically smooth.
The cell generally includes a sample entrance port and a sample exit port. The cell generally also includes a light input port in optical communication with a light source assembly. The cell further generally includes a fluorescent light detector port in optical communication with a detector/analyzer assembly. The cell further generally includes a reaction chamber having interior surfaces or a reaction chamber insert. Generally, the interior surfaces are reflective to a desired frequency range of light such as the UV region of the electromagnetic spectrum associated with the compound or compounds to be analyzed. Preferably, the interior surfaces are highly reflective and highly polished or optically smooth. One part of the highly reflective interior surfaces are constructed to reflect fluorescent light emitted away from the detector port towards the reflector port, increasing the fluorescent light into the detector/analyzer assembly. The fluorescent light reflective portion of the interior surfaces can also be constructed to focus fluorescent light emitted away from the detector port into the port. Another part of the highly reflective interior surfaces can be constructed to reflect the excitation light passing through the chamber back into the chamber increasing the excitation light concentration in the chamber. The excitation light reflective part of the interior surfaces can also be constructed to reflect and focus the excitation light into a central region of the chamber. Highly reflective and optically smooth surfaces increase a signal-to-noise ratio of the detector and improve both sensitive and detection limit of the detector.
The present invention also provides a fluorescent instrument which includes a sample delivery system, a light reaction cell as described above, a light source, and a fluorescent detector/analyzer system.
The present invention further provides a method for improving sensitivity and detection limits of fluorescent detectors and instruments by contacting a sample with light in a reaction cell as described above.